In welding metal sheets together from only one side, originally, metal backup bars were used which had inherent limitations in certain situations, as stated by John Cresap, in 1962 or 1963 in his article entitled, Fiber-Glass Tape for Backing Up Welds, refer to NASA Bulletin SP501F. To overcome these limitations, he described how fiberglass tape was being tested as a substitute for metal backup bars. However, as early as 1944, U.S. patent disclosures describe how previous inventors have provided various improved backup materials in lieu of metal backup bars. Some of these disclosures are as follows:
In 1944, E. A. Smith in his U.S. Pat. No. 2,362,505 set forth an improved backing strip, used during welding, combining a flexible refractory material and a flexible metallic support to carry the refractory material. In 1958, Messrs, Chyle and Zimmermann in their U.S. Pat. No. 2,820,427 provided a welding backup assembly of a tape made of fibrous glass fabric impregnated with a thermo-plastic, pressure sensitive adhesive. Also Messrs. Chyle and Zimmermann in 1959 in their U.S. Pat. No. 2,916,001 provided a welding backup strip comprising a thin layer of ceramic or refractory insulating material extruded or otherwise applied to a wire mesh or lattice.
Messrs. Hackman and O'Brien in 1961 in their U.S. Pat. No. 3,001,057 in respect to sigma spot welding used a backing strip of glass or silica having its own heat resistant adhesive. In 1965, Messrs Duffy and Flannagan in their U.S. Pat. No. 3,192,357 used a combination of an immediate fiberglass tape to be adjacent the weld to be made, and this tape in turn is backed up by a reinforced strip of bonded flex materials. In 1968, Mr. Cornell in his U.S. Pat. No. 3,372,852 described his welding backing tape composed of refractory material in a bonded strip secured with a heat resistive adhesive, to a glass fabric strip. In 1968, Mr. Kuder in his U.S. Pat. No. 3,365,566 described a backup tape, used during welding, comprised of glass cloth with an adhesive to secure along the center a thin layer of metal or foil and also to secure the tape to the bottom piece of metal to be welded to another piece of metal.
In 1970, Mr. Cornell in his U.S. Pat. No. 3,494,020 described a welding backup tape having a backing made of glass fabric, metal foil, paper, cotton, nylon, rayon, treated with a flame retardant composition, and a centered strip of refractory material containing a carbon scavenger, and including an adhesive. In 1975, Mr. Keith, in his U.S. Pat. No. 3,929,270 describes a welding backup tape having a strip of flexible refractory material centered on tape backing of glass cloth, metal foil or the like having a pressure sensitive adhesive, and this preassembly is improved by adding a tacky layer of film-forming adhesive, covered in turn by a monolayer of inorganic particles. In 1976, in another of his patents, U.S. Pat. No. 3,972,466, Mr. Keith discloses an improved high temperature welding backup strip. On a woven carbon cloth, having a pressure sensitive adhesive, a refractory layer of glass cloth is centered to form the first embodiment of his backup strip. In another embodiment, refractory particles are included of aluminum oxide, glass, and mixtures thereof bonded together.
Then in 1977 Messrs. Roden and Criger in their U.S. Pat. No. 4,049,183 described their use of a heavy wall, flexible, woven refractory fiber tube placed within a slightly larger diameter similar tube with both tubes being partially flattened against an adhesive coated surface of a wider, heat resistant strip to complete their welding backup tape. It is understood, more recently Messrs Roden and Criger have created the equivalent of their tube in another way.
Later in 1977, the applicant developed an improved welding backup tape having a carrier tape or carrier, which did not have any aluminized backing, or the like, which, otherwise, would have trapped gases liberated from adhesives and other materials during welding to possibly create voids in the welds, and which, in reference to the two concentric tubes, i.e. sleeves, used by Messrs. Roden and Criger, provided an outer tube or sleeve made of finely woven fiberglass, to create a back weld surface, which was smooth enough not to interfere with otherwise obtaining a 100% X ray testing of the weld, then having only a minimum pattern imparted to the weld surface by the finely woven fiberglass of the outer tube or sleeve. However, the finely woven fiberglass tube or sleeve, although in many instances resulting in a 100% X ray test result, did in other instances, because of its thinness, split apart and/or burn, often yielding tramp fiberglass splinters, i.e. shards, to the resulting weldment as unwanted inclusions. Therefore efforts were continued to create a better welding backup tape.